1. Field of the Invention
The present invention is directed to an X-ray diagnostic installation for mammography examination of the type having an arm for an X-ray tube, a holder for an image receiver and a subject table, the holder and the subject table being laterally adjustable relative to one another, as well as having a compression plate arranged between the X-ray tube and the subject table, the compression plate being connected to and displaceable along the arm, and wherein the arm is rotatable around a horizontal shaft attached in a stand.
2. Description of the Prior Art
It is advantageous in a mammography examination when the size of the image receiver is adapted to the size of the subject table. In those instances wherein the image receiver is an X-ray film applied in a cassette, there are two standard cassette sizes in the marketplace, namely a larger X-ray film cassette having the dimensions 24xc3x9730 cm and a smaller X-ray film cassette having the dimensions 18xc3x9724 cm.
One possibility that is practiced is disclosed in U.S. Pat. No. 4,613,982, is to have a subject table for each cassette size, the width of the subject table corresponding to the width of the cassette. In this way, the user can change between the cassette sizes dependent on the size of the subject. Having multiple of subject tables, however, is comparatively expensive and changing the subject table can be time-consuming.
The reason why the width of the cassette or of the X-ray film should be the same as the width of the subject table is so that, in a lateral exposure, the subject table and thus the X-ray film as well can be displaced into the armpit of the patient so that as much breast tissue as possible is imaged.
In conjunction with an X-ray diagnostic installation of the type initially described, that is disclosed in U.S. Pat. No. 4,989,227, a proposal is made to simplify the mammography examination and to reduce the costs by only one subject table being employed for the X-ray film cassettes that differ in size. The subject table, which is secured to the arm for the X-ray tube, has a width that corresponds to the width of the larger of the two standard cassettes. In a lateral exposure, the desired imaging of the breast tissue is therefore established with a larger X-ray film cassette present in the subject table.
Given employment of the smaller cassette, the arrangement in the subject table disclosed in said U.S. Pat. No. 4,989,227 can be used to shift it into three fixed positions, namely a centered position wherein the cassette is attached so as to be spaced from the end sides of the table, a position wherein the one end side of the cassette lies along one side of the subject table, and a position wherein the other end side of the cassette lies along the other side of the subject table.
For a vertical exposure of the breast, the cassette is attached in the centered position. For a lateral exposure, the subject table is rotated around the horizontal shaft with the above-described arm so that the subject table is pushed into the armpit of the patient. In this position, the cassette in the subject table is shifted into a position wherein the upper end side of the cassette lies along the upper side of the subject table. In combination with a displacement of the cassette in the subject table, the radiation field of the X-ray tube no longer covers the entire surface of the cassette or the X-ray receiver. For a lateral exposure, a setting of the diaphragms of the X-ray tube must be undertaken anew, which is relatively time-consuming. This can be unpleasant for the patient and somewhat painful since the breast is clamped between the subject table and the compression plate.
An object of the present invention is to provide an X-ray diagnostic installation of the type initially described wherein the image receiver can remain located in the X-ray field with simple and thus inexpensive means given rotation of the subject table or of the image receiver from a vertical attitude into a lateral attitude.
This object is achieved in an X-ray diagnostics installation of the initially described type wherein the holder for the image receiver is connected to the arm, and the subject table is fashioned to be laterally displaceable relative to the holder. Because the holder for the image receiver is connected to the arm, the image receiver remains in the X-ray field in all positions of the arm. In conjunction with a lateral exposure, i.e. when the image receiver is pushed into the patient""s armpit, the subject table is shifted into a position wherein the upper side thereof lies along the short side of the image receiver. An exposure can now be made relatively quickly.